4.0 trashed idol/stalling issue

Alright, im belly up guys.

I need some help, some suggestions, some input, some ideas.. I need it all. Whatever i can get.


97 cherokee sport
4.0, auto trans

It will randomly idol like complete crap, if i dont play with the gas pedal it will end up stalling.
This happens in gear, while coasting down a hill in gear, while sitting still in park or neutral.
This also happens immediately after starting it up when it is cold, it'll happen when its running at 210 degrees and its been running for hours.
Like i said, this problem is completely random.


I have a video of it idoling really rough like .
https://www.youtube.com/watch?v=w9uLqHHFyM0


Now, here is what i have replaced..

Distributor Cap
Rotor
Spark Plugs
Spark Plug Wires
Map Sensor
Crank Sensor


I have a new TPS but i have not installed it yet.
I was going to replace the IAC sensor also, however NAPA in Attica did not have one available.

Fuel system info..
Fuel Cell, Ford crown vic inline pump, stock fuel line, stock fuel return line.



This is my trail rig, doesnt get driven on the street at all.

My opinion would be a vacuum leak. Check the throttle body bottom gasket, the intake manifold to head gasket, and the power brake booster.

Pull the throttle body and clean the passages with carb cleaner before replacing the IAC.

I'll check it out.


i can lightly spray starting fluid around those areas to check for vacuum leaks, correct?

A bad TPS can cause all sorts of idling problems, along with the IAC.
Since you have a new TPS, try it. It only takes a few minutes to install it.

Yeah i havent got to the TPS yet.

I was out at the offroad park while replacing said sensors.
Skipped the TPS because the 2 bolts seemed seized and i didnt want to snap them.
Wanted to wait until i got home to hit them with some PB.

I'll get the TPS replaced and post up my results.

Check timing first, then upgrade to neon injectors and clean the intake manifold and throttle body. Also check for clogged catalytic converter if you have one.

If the timing is off, isnt it going to run like crap all of the time?
Same for the catalytic converter..

You can't generally adjust the timing on a MPI 4.0L, so don't bother checking it if you haven't done anything to change it.

Did you clean the IAC? I agree with old_man. Vacuum leak, IAC or TPS.
Unfortunately...all the things you haven't tried. Cleaning the IAC should be done gently with carb cleaner and a Q-Tip.

I'm going to second the TPS. I have had parts store TPSs fail out of the box, go OEM if you can.

Like i said... Its completely random.

Tonight the 4.0 received a brand new TPS and a brand new IAC.
The IAC that i removed was filthy.
Im not sure what they should look like once used.. This one however was caked in black stuff.

I bought a fuel pressure gauge, so once it gets here i'll check to make sure my fuel pressure is steady and up to par.

Going to check for vacuum leaks tomorrow.

Well, didnt find any vacuum leaks. not even any tiny ones.

I literally went through about half a can of starting fluid.
Sprayed the base of the injectors, the intake gasket, all of the vacuum lines that i could see. Even soaked the black canister on the passenger side fire wall.

Is the idle higher than normal ? From video it looks high, maybe not can't see it good. If so, hunt down that vac leak. Just one at a time start plugging a vacuum source, see if helps. I say that cause the old starting fluid is not very accurate IMHO. Probably not with your intermittent problem but it don't hurt to check the torque on those manifold bolts.

Another thing I notice is the motor seems to be shaking hard like more than 1 cylinder is not firing. That puts you up for testing injectors. You can pull the plug on injectors one at a time and see what makes a difference. Or get a noid light and test. The computer should throw a code if this is the case, maybe not.

The IAC will get dirty like that, usually you can just clean it gently. But that black crud is also in your throttle body cavity where that IAC sits. I do a TB cleaning and IAC cleaning at the same time myself. And a new base gasket.

Just wondering what you found out?

I noticed something in the video. When you had your phone near the air filter box the suction noise seamed excessive. The only reason i mention that is I have a jeep project that is doing what looks to be the same thing. I noticed with mine when it is idling normal you can't hear much if any vacuum hiss coming from the air box, and when its choppy and trying to hold an idle its hissing incredibly loud. So loud that when I pull the intake hose off the TB its uncomfortable to listen to vs when it is at a normal no problem idle. Makes me think that the IAC is working correctly and trying to open up to recover the low idle.

I'm thinking mine could be a fuel problem since the the PCM is trying to correct for the idle problem. I would think that if its getting enough fuel it would be reving way to high with the IAC opening that far.

Another thing that makes me think its fuel is, if i pull the #1 injector plug off i can't tell much of a difference, also when i plug it back in the idle smooths out and goes back to normal???

Looks like i'll have to pick up a fuel pressure test kit and see what i can find out.